When a covered or uncovered conductive wire is being sewn to an object with embroidery thread by using a sewing machine, it sometimes happens that, owing to some abnormality such as malfunction of the machine, etc., a needle of the sewing machine comes into contact with the conductive wire directly or through the covering material, thereby damaging the conductive wire. The damage leads to insulation failure, conduction failure, breaking or like failures of the covered or uncovered wire. The damaged wire has little or no commercial value.
No apparatus has so far been developed which warns the operator of the damage to a covered or uncovered conductive wire caused by contact with a needle of a sewing machine. Accordingly, the covered or uncovered conductive wire is conventionally inspected for defects after having been sewn to an object or article. Specifically stated, the wire sewn to the object is tested with a conductivity tester for conduction failure, breaking or like failures, and, in the case of a covered conductive wire, visually checked for insulation failure (flaws on the covering material). When the conductive wire to be sewn is a heating wire, defects can be detected by inspecting the wire for anomalous local heat generation. The above inspection methods, however, are troublesome and often fall to detect conduction failure, breaking or insulation failure. The change of detection is particularly low in the inspection of stranded wires which are comprised of a plurality of fine wires.